Background: Streptococcus mutans is plaque-forming initiator bacteria. Plaque on the surface base of denture can cause color changing, bad breath, inflammation, and infection called denture stomatitis. Denture hygiene must be maintained by denture soaking in 0.2% chlorhexidine gluconate. However, 0.2% chlorhexidine gluconatethat used incessantly can cause side effects such as the changing of denture color and the fading of denture base pigmentation. The ironwood stem bark extract can be an alternative for denture cleanser material. Objectives: To analyze the effect of ironwood stem bark extract on the growth of Streptococcus mutans on heat cured type acrylic resin denture plate. Methods: True experimental laboratories research was used with post test only control group design using 9 treatment groups which are 5%, 10%, 20%, 40%, 60%, 80%, 100% concentration of ironwood stem bark extract, 0.2% chlorhexidine gluconate and aquadest. The treatment was performed with 3 times repetition resulting in 27 total samples. Antibacterial activity was measured by calculating the bacteria colony number. Results: The 5% and 10% concentration of ironwood stem bark extract were effective in reducing Streptococcus mutans with30.3 CFU/ml and 10.3 CFU/ml average colony number. The ironwood stem bark extracts with 20%, 40%, 60%, 80%, 100% concentration are effective and equivalent to 0.2% chlorhexidine gluconate against Streptococcus mutans with 0 CFU/ml average value. Conclusion: The 20%, 40%, 60%, 80%, 100% concentration of ironwood stem bark extract is equally effective as 0.2% chlorhexidine gluconatein killing Streptococcus mutans,exhibiting potential to be an alternative for denture cleanser material.Keyword: 0.2% Chlorhexidine gluconate, ironwood stem bark extract, acrylic resin denture plate heat cured type, Streptococcus mutans.